The response of the guinea pig cochlea hair cells to the electrical stimulation of the crossed olivocochlear bundle will be examined. The results will be used to define the site and mechanism of action of the inhibitory transmitter substance of the crossed olivocochlear bundle. In addition, an attempt will be made to mimic the recorded responses by the microelectrophoretic application of chemicals proposed as the inhibitory transmitter substance. This will be done to aid in defining the identity of the transmitter substance. BIBLIOGRAPHIC REFERENCES: Bobbin, R.P. Recording site in the organ of Corti determined by an electrode-marking technique. Arch. Otolaryngol., 102:45-48, 1976. Bobbin, R.P. and Gondra, M.I. Effect of nicotine on cochlear function and noise-induced hair cell loss. Ann. Otol., Rhinol. Laryngol., 85(2):247-254, 1976.